The present invention relates to the use of masterbatches of polyarylene-amide resins, in which the polyamide resin is dispersed finely and in a stable manner in a matrix of an aromatic polyester resin, in the preparation of polyester resins to which the polyarylene-amide resin is added in quantities smaller than those present in the masterbatch.
It relates in particular to the use of masterbatches in the preparation of polyester resins suitable for the manufacture of containers having good gas-barrier properties.
Aromatic polyester resins, particularly polyethylene terephthalate, are used in ever increasing quantities in the production of beverage containers. Since the gas-barrier properties of these resins are not good enough to keep beverages, particularly carbonated beverages, unchanged for sufficiently long periods, attempts have been made to improve their barrier properties by adding to them polyarylene-amide resins, in particular poly(m.xylylene adipamide) (poly-MXD-6) which, as is known, have particularly good barrier properties.
However, polyarylene-amide resins are not compatible with aromatic polyester resins so that the dispersion obtained by mixing the two resins in the molten state does not enable best use to be made of the gas-barrier properties of the polyarylene-amide resins.
A good dispersion of the polyarylene-amide resin can be achieved in accordance with the method described in EP-A-964031 in which the polyester resin is premixed in the molten state with a dianhydride of a tetracarboxylic acid, in particular pyromellitic dianhydride (PMDA), used in quantities of less than 2% by weight, and the polyamide resin is then added, also in the molten state.
The mixtures thus obtained have good properties of impermeability to oxygen and carbon dioxide.
The production of containers (bottles) from polyester resins to which polyarylene-amide resins have been added involves the preparation, from time to time, of mixtures suitable for the requirements of individual users, in dependence on the particular requirements of the bottle manufacturer, resulting in wasting of energy and inefficient use of production plants.
The availability of masterbatches of polyarylene-amide resin for use by container manufacturers, in dependence on their requirements, could solve the problem, provided that the microstructure of the masterbatch were retained upon its dilution in the molten state with the polyester resin, and that this structure were also retained upon the subsequent processing of the resin for the production of containers and/or for other applications.
It has now unexpectedly been found that masterbatches of aromatic polyester resin containing from 10% to 40% by weight of polyarylene-amide resin, in particular, poly-MXD-6, prepared in accordance with the method described in EP-A-964031, can be diluted with the polyester resin and the resin thus obtained, containing the polyamide in concentrations of less than 15% by weight, can subsequently be processed without thereby compromising the stability of the dispersion of the polyarylene-amide resin.
It has in fact been found that the dispersion of the polyarylene-amide resin in the polyester matrix in the form of domains with average dimensions of less than 1 micron not only remains unchanged after dilution with the polyester resin but, in some cases, is further improved as a result of a reduction of the average size of the dispersed particles.
The microstructure indicated above is also maintained in the manufactured products.
The above-described result is unexpected, bearing in mind that the masterbatches rich in polyarylene-amide resin which are described in EP-A-964031 (containing more than 50 and preferably 80-90% by weight of polyamide resin) separate into phases when they are diluted with the polyester resin.
The polyester resins usable in the preparation of the masterbatches, as well as those to which the masterbatches are added, are produced by polycondensation by known methods, of dicarboxylic aromatic acids, preferably terephthalic acid with diols having 2-12 carbon atoms, such as ethylene and butylene glycols and 1,4 dimethylolcyclohexane.
Preferred resins are polyethylene terephthalate and copolyethylene terephthalates in which up to about 20% in moles of terephthalic acid units are replaced by units derived from isophthalic acid and/or naphthalene dicarboxylic acids.
Copolyethylene terephthalates containing up to about 5% of isophthalic acid units are preferably used in the preparation of the containers and bottles.
The intrinsic viscosity of the polyester resins used in the preparation of the masterbatches is generally between 0.3 and 0.7 dl/g.
After mixing, in the molten state, with the dianhydride of the tetracarboxylic acids and subsequent addition of the polyamide resin, the intrinsic viscosity may be brought to values greater than 0.7 dl/g, for example, between 0.8 and 1.2 dl/g, by polycondensation in the solid state (SSP) operating in accordance with known methods, at a temperature of about 170 to 220xc2x0 C.
The treatment in the solid state is preceded by a crystallization stage, also carried out in accordance with known methods.
The mixing of the resins, in the molten state, with the dianhydride of the tetracarboxylic acid is carried out with the use of single-screw or twin-screw extruders with relatively short residence times in the extruder (generally less than 180 seconds), operating at temperatures from 270xc2x0 to 300xc2x0 C.
The polyarylene-amide resin is mixed, in the extruder, with the polyester resin, premixed with the dianhydride, or is added directly into the extruder for mixing the polyester resin and the dianhydride, in a zone downstream of the premixing zone.
The masterbatches contain from 10 to 40% by weight of the polyamide resin. Quantities greater than 40% by weight are not of practical use since they involve extrusion difficulties.
The polyarylene-amide resins usable are obtained from aryl diamines and from dicarboxylic aliphatic acids with 6-22 carbon atoms, preferably adipic, suberic and dodecanoic acids.
Poly-MXD-6 is the preferred resin.
The average numeral molecular weight of the resin is generally between 8,000 and 50,000.
Polyamides with crystallization rates similar to that of the polyester resin are preferred.
The terminal NH2 groups of the polyamide may be reacted with epoxy compounds or with aliphatic anhydrides to improve their dispersibility in the polyester resin.
The dianhydrides of tetracarboxylic aromatic acids are preferred; pyromellitic dianhydride is the preferred compound. Other examples of dianhydrides are dianhydrides of 3,3I,4,4I-benzophenone tetracarboxylic and 2,2bis(2,4-dicarboxyphenyl)ether acids.
Trimellitic anhydride and similar anhydrides can also be used: the obtained masterbatches present a fine dispersion of the polyarilene amide in the polyester matrix, which remains substantially unchanged after dilution of the masterbatch with the polyester resin and in the manufactured articles thereof.
The intrinsic viscosity of the resin is measured in a solution of 0.5 g of resin in 100 ml of an 80/40 by weight solution of phenol and tetrachloroethane, at 25xc2x0 C. in accordance with ASTM D 4603-86.
The following examples are provided by way of non-limiting illustration of the invention.